The present invention relates generally to an anode member in use for a variety of electrolytic treatments, and particularly to an anode member such as rack means on which products of aluminum or aluminum alloy (hereinafter referred to as aluminum material) are suspended for anodic oxidation treatment.
Hitherto pure aluminum or aluminum alloy is mainly used as anode member for anodic oxidation treatment of products of aluminum material and in a specific case titanium is used for the same purpose to some extent. Aluminum material as anode member, however, has drawbacks as described below. Namely anode member immersed in the electrolyte is anodized together with the aluminum products, since the former is made of the same material as the latter. This causes high electric power loss, because the anode member has current flow-out therefrom at almost the same current density as the aluminum products. As the anode member is subjected to anodic oxidation treatment, it has an anodized film formed on the surface thereof in the same manner as the aluminum products.
Since the anodized film has no conductivity, the film should be removed prior to reusing the anode member so as to assure electric contact. In practical operation this non-conductive film may be dissolved using alkali. Alternatively, removal of the non-conductive film may be carried out at the same time as degreasing, chemical polishing or the like is performed as pre treatment. Due to a fact that formation and removal of the anodized film are repeated over the anode member of aluminum material every time when aluminum products are anodized, resulting in gradual wearing thereof, it becomes necessary that the anode member is replaced with new one, even though it has still mechanical strength sufficient to carry the aluminum products thereon. As a result cost of anode member in total operation cost is not negligible. Moreover it is to be noted as another problem that a considerable quantity of chemicals is consumed for removal of the anodized film.
On the other hand, in case that titanium is employed for anode member, it has very thin anodized film which is generated during anodic oxidation and this anodized film is easy to be broken away by means of force caused in the course of racking for the aluminum products. Thus different from the anode member of aluminum which requires removal of anodized film prior to anodic oxidation treatment, the anode member of titanium has no requirement of removal of anodized film, which enables the anode member of titanium to be repeatedly utilized for a long period of time. Further titanium anode member has very little current flow-out therefrom during anodic oxidation treatment, whereby it has power loss remarkably less than that of aluminum. For the reasons as mentioned above titanium is important material for racking member in use for heavy aluminum products, elongated aluminum products such as aluminum sash or the like as well as anode member for anodic oxidation at high current density, because anode member of titanium has a variety of advantages over that of aluminum and additionally has a substantially high springiness in comparison with the latter.
In spite of the excellent advantage of less wearing during anodic oxidation treatment, however, the anode member of titanium has a drawback that it is subjected to hydrogen embrittlement which is caused by environmental corrosion (mainly corrosion by sulfuric acid) during serial processes of anodic oxidation treatment. Thus it is pointed out as a disadvantage in practical use as anode member that titanium anode members may be broken or damaged in racking because of the aforesaid hydrogen embrittlement as they are repeatedly used.
As mentioned above, the conventional anode member of aluminum or aluminum alloy or titanium has drawbacks inherent thereto and accordingly fails to meet all requirements for anode member.